In a high-capacity power conversion equipment such as a high voltage direct current (HVDC) system or a static VAR compensator (SVC) system for improving voltage stability and compensating for reactive power, system harmonic waves and unbalance have influence on system control. In particular, in the case of an SVC system, non-characteristic harmonics may abnormally increase due to single-phase faults such as unbalance in current or voltage between phases and ground fault of a power interconnection system. Therefore, these systems require a high-performance and a high-precision control scheme.
However, in control of a general SVC system, since a three-phase root mean square (RMS) value of a power system is mainly controlled by operation of a three-phase voltage and current, there is difficulty in compensation for an unbalance condition due to disturbance and faults.
Accordingly, when phase unbalance occurs in a transient or faulty state of a power system, there is a need for a method of compensating for phase unbalance to improve stability of an SVC system.